1. Field of Invention
The present invention relates to the field of wireless communication, in particular to method and system supporting handover from macro Node B to home Node B which enables the home Node B to be better incorporated into conventional wireless mobile networks.
2. Description of Prior Art
In a wireless mobile network system, indoor coverage always plays tough for network operators. On the other hand, demand for superior indoor coverage is getting stronger. It has become a critical issue about how to effectively settle the contradiction between indoor coverage and capacity while satisfying requirements of voice and data services. This requires any necessary solution for wireless network coverage. Meanwhile, there is technical tendency and demand for the incorporation of the wireless mobile network technique and other techniques.
Such tendency and demand give birth to home Node B, which is a new type of Node B with small volume and light weight and can be placed anywhere indoor according to a user's requirement. RJ45 is adopted as the physical interface of the home Node B. Through network wire, it communicates with RNC by bearing mobile network protocol on TCP/IP protocol. Therefore, the home Node B integrates the mobile network with the Internet and thus extends the mobile network's Node B into homes, so that mobile network's coverage and service are broadened. An indoor user can occupy the entire radio resources of the home Node B. The home Node B is an important stage in the evolution of future network integration.
Since a home Node B is an indoor small base station, it has characteristics, such as greater quantity, smaller coverage area, etc., compared with a conventional macro Node B. So, it is necessary to further perfect techniques and methods for handover from macro Node B to home Node B. And in present invention, a method for supporting handover from macro Node B to home Node B is proposed.
Since the home Node B is novel, the handover from macro Node B to home Node B is a hot spot in study and research.
A conventional macro Node B has characteristics of wider coverage, fixed site location, static configuration and no changes after service accessing. The characteristics of wider coverage and fixed site location impose a limit on the number of neighboringing cells to the macro Node B. So, there exists no case where different neighboring cells share the same scrambling code. In other words, Pi in the following neighboring cell list are different from one another.
PrimaryscramblingNo.codesCell_ID. . .. . .1P115014. . .. . .2P210064. . .. . .. . .. . .. . .. . .. . .NPn07128. . .. . .
In addition, thanks to static configuration, the engineering staff can manually configure an neighboring cell list for every cell according to the network planning in the initial stage of network establishment. Once the configuration has been done, it is generally not necessary to make any change to the established network. Basically, there will be no change. After the network is put into operation, RNC looks up the neighboring cell list according to the primary scrambling code Pi contained in a measurement control message reported from a terminal so as to uniquely specify the corresponding cell's Cell_ID.
However, great change has been taken place after the home Node B is introduced. The home Node B is intended to offer services to home subscribers. That means home Node B can access or exit services at any time. In this way, the home Node Bs surrounding a macro Node B are continuously changing. It is impossible to manually configure the neighboring cell list for a macro Node B in the initial stage of the network construction, since a lot of home Node Bs may locate around one macro Node B, and the reuse of a primary scrambling code may happen among these home Node Bs. If a home Node B is not yet configured in the neighboring cell list of the macro Node B, a terminal will not measure a corresponding signal from the home Node B. Therefore, the UE can not handover from the macro Node B to home Node B, or even can not implement cell reselection normally.
In real applications, the operators hope to implement the function of handover from a macro Node B to a home Node B so as to guarantee the call service quality and service requirement for enterprises. By far, no final scheme on the handover from macro Node B to home Node B has been specified by any relevant standardization organization. No perfect solution is figured out to settle this problem. How to implement the handover from macro Node B to indoor small Node B becomes a hot spot to operators and equipment providers.
As described above, the neighboring cell list of a macro Node B in conventional network is configured manually according to the network planning and can not be updated automatically. So, it is impossible for a macro Node B to add or delete the information on a home Node B into/from the neighboring cell list in real time, since a home Node B cell is possibly established or removed arbitrarily. In this case, UEs in the macro Node B can not detect any signal from the home Node B, and thus they can not handover from the macro Node B to the home Node B. Similarly, trouble occurs at cell reselection.
By far, no final scheme on the handover from macro Node B to home Node B has been specified by any relevant standardization organization. No perfect implementation design has been proposed by any company. During the commercial application of home Node B, it is yet not possible to implement handover from macro Node B to home Node B. It is challenging to users who get used to common communication mode of handover. And also, the operators hesitate to accept home Node B. These facts greatly affect the application and popularization of home Node B.
Even if the macro Node B could update the neighboring cell list in real time, problems may rise during the addition or deletion of neighboring cells according to the access condition of home Node B. Some companies have proposed such method that when a home Node B powers on, the macro Node B's neighboring cell list is updated automatically so that the information of the accessing home Node B can be added to the macro Node B's neighboring cell list. This scheme may be effective in the case of a small number of home Node Bs which are not widely applied. Since a home Node B is in unit of home, having a small coverage area, and there are usually a great number of home Node Bs, many problems may occur during the commercialization of the home Node B. Examples of problems are listed below.
A) There is generally a high density of home Node Bs located in the coverage of a macro Node B. If all the home Node Bs were added to the neighboring cell list of the macro Node B, the neighboring cell list would be very cumbersome and exceed the upper limit regulated in the existing rule (e.g., at most 32 co-frequency neighboring cells and at most 32 hetero-frequency neighboring cells).
B) To break the limit of 32 neighboring cells, it is necessary to modify SIM (subscriber identity module) card. This will cause the most and even unacceptable effect to users. In addition, the memory capacity of SIM is limited. Even though the limit of 32 neighboring cells could be broken, if a lot of home Node Bs locate within the coverage of a macro Node B, reuse of a primary scrambling code will happen among part of the home Node Bs. For a conventional macro cell, each primary scrambling code in the neighboring cell list is uniquely allocated. Therefore, the macro cell can determine a Node B corresponding to the unique primary scrambling code reported from a terminal. If reuse of a primary scrambling code happens, the handover from the macro Node B to a home Node B would fail, for the macro Node B could not distinguish which home Node B the UE should be switched to according to such reused primary scrambling code, when the UE initiates the handover process.
C) Frequent access or exit of home Node Bs may result in waste of system resource, since the macro Node B has to frequently update the neighboring cell list and thus great deal of signaling is generated. If bursts of great deal of signaling arrive at the system at the same time, heavy system burden will be a great challenge to the capacity of existing system, and even affect the existing system's normal operation of fundamental services.
The problems mentioned above can be easily triggered in commercial network environment. Thus, the problem of handover from macro Node B to home Node B can not be well settled for commercial networks, with the method of updating the macro Node B's neighboring cell list in real time.